1. Field of the Invention
This invention relates to an improvement for a catheter-type electrode member for an implantable pacemaker, insertable from without through the epicardium into the heart muscle for cardiac stimulation, with regard to the electrode member disclosed in my U.S. Pat. No. 3,978,865, granted on Sept. 7, 1976. Similarly as in my earlier patent, the improved electrode member of the present invention is to form part of an implantable pacemaker, for conveying electric stimuli to the epicardiac and eventually to the intramyocardiac zone of the heart, upon energization by an electric pulse generator.
2. Description of the Prior Art
A comment about the conventional catheter-type electrode members has already been made in my above cited patent, so that repetition becomes unnecessary, it being sufficient to point out that in those known conventional electrode members it was necessary to suture the platform to the heart muscle, after insertion of the conductor into at least the epicardium, to prevent any dislodgment of the tip of the conductor by the beating movement of the heart muscle.
The catheter-type electrode member of the aforementioned U.S. Patent provides for the insertion of the conductor into the epicardium without requiring any additional surgical intervention to suture the platform to the heart muscle. While this catheter type electrode member operates satisfactorily when inserted by a skilled surgeon, practice has shown that when the electrode is used by a surgeon who has not yet carried out a sufficient number of operations in this particular field and bearing in mind that the surgeon has to implant the hook shaped member which is the electricity conducting member in the patient's heart muscle while the heart is beating, it may be that the forward movement of the hook shaped electricity conducting member becomes barred due to special pathological circumstances of the heart. Thus, the tip of the hook will not be facing the major surface of the platform upon concluding the insertion into for instance the epicardium thereby tending to straighten the hook. In this event the continuous beating movement of the heart may eject the hook from the heart. To avoid this, as a safety measure, the platform according to the present invention, is provided with at least one generally straight shaped needle-like anchoring means projecting from the same flat major surface of the platform from which also the hook projects and said needle-like anchoring means projects at such an angle that its axis crosses at an acute angle the tangent line passing the generally semicircular shaped hook at the point of connection of the latter with the conductor, which is usually a helically coiled portion, which sligthly projects out of said flat major surface of the platform. Because of such crossing arrangement of the two parts hereinabove described, a positive lock is forwarded, so that the tendency ejecting the imperfectly located hook becomes barred, as soon as the platform, due to its resiliency will become in abutting relationship with the outside face of the heart muscle and thereby also inserting the anchoring means into the epicardium, as will be better understood later on.
In some prior art devices the electrode comprises a platform which instead of being sutured with suture string, has at the edges of the platform a plurality of spaced apart hook-shaped anchoring needles. These hook-shaped anchoring needles do not operate in combination, as far as the anchoring is concerned with the actual electrode member, which is always a straight member, so that there is no interaction, as in my proposed invention, of the anchoring means with the actual conductor of electricity. In other words these known hook-shaped needles are hooked into the heart, once the electrode has been inserted. These needles have to provide sufficient force to retain the platform against the outside face of the heart muscle, to assure that the straight conductor will not move within the perforated portion of the epicardium. In practice it can not be avoided that in those arrangements, which are not of the safest type, the tissues of the heart muscle become damaged due to an unavoidable amount of movement of the actual electricity conducing conductor inserted with it straight end portion in the epicardium. In addition, it is extremely difficult to properly locate these known types of electrodes, because while the heart muscle is beating, the latter has to be perforated to insert the straight electrode tip and then it has to be maintained by hand in the inserted position, while each of the hooks at the edge portions of the pad has to be anchored by separate steps.